The present invention relates to the technical field of dyeing textile materials.
A large proportion of the impacts caused by the textile industry is due to present-day dyeing and finishing processes, which consume large amounts of water and textile auxiliaries. All that continued optimization of existing processes could hope to achieve appears to be at best a marginal improvement with regard to minimizing environmental impact.
Dyeing denim articles with indigo is of particular interest in this context, since this art usually utilizes large-scale industrial dyeing ranges that have large capacities and thus also large water requirements and wastewater impacts.
State of the art involves a continuous exhaust dyeing process to dye individual threads made up in the form of a sheet of threads (warp threads), as needed for weaving, or in the form of a rope which combines 300 to 400 warp threads in one rope. In this continuous exhaust dyeing process, the substrate is continuously led through the dyebath (hereinafter also referred to as liquor) and, before attainment of the concentration equilibrium, separated again from the liquor. After this separation, the dye which has already gone onto the warp threads is oxidized to convert it into its insoluble form and thereby fixed on the substrate. In the further course of the dyeing process, the warp threads are again introduced into the liquor and the exhaust process starts once more. The oxidized dye already present in the warp threads does not take part in this renewed dyeing operation, and therefore a further “layer” of reduced dye can exhaust from the liquor onto the warp threads above the oxidized first layer of dye. This buildup layer by layer ultimately makes it possible to achieve a high concentration of the dye on the warp threads.
These processes are carried out for warp threads in open-width dyeing machines and for ropes of threads in rope dyeing machines, which involve liquor volumes of 5000 to 7000 liters and have appreciable requirements in terms of heating energy, electricity and processing chemicals.
In addition, the low fastness level achieved with existing processes of dyeing denim with indigo is an irksome problem for the industry and for the consumer, particularly in relation to dry and wet rub fastnesses.
Finally, the processes mentioned are technically demanding in that a multiplicity of mutually interacting parameters have to be captured and policed at great cost and inconvenience in terms of the measuring and control technology needed.
There is accordingly an appreciable demand for dyeing processes for dyeing textile material which require distinctly less water and energy, are technically simpler to handle and yet provide dyeings of better quality.
The present invention, then, provides a process which leads to a distinct reduction in water and energy requirements and which generates less textile waste. This makes it significantly more environment-friendly and economical than existing processes. The process of the present invention, what is more, leads to a distinct increase in fastnesses, particularly rub fastness.